No abstract

ABSTRACT. Genetic diversity and population differentiation of the blue swimming crab, Portunus pelagicus, in Thailand were analyzed by RAPD analysis. One hundred and twelve RAPD fragments were generated from 109 individuals of P. pelagicus using OPA02, OPA14, OPB10, UBC122, and UBC158 primers. The percentage of polymorphic bands in each geographic sample and that of each primer across overall samples were 72.7-85.0 and 92.0-100%, respectively. Large numbers of polymorphic bands found in the RAPD analysis suggested high genetic diversity of Thai P. pelagicus. The mean genetic distance between samples across all primers was 0.0929-0.2471. Significant geographic heterogeneity was observed across samples overall and between all pairs of geographic samples (P < 0.01 for θ and P < 0.0001 for the exact test), indicating strong genetic differentiation of P. pelagicus in Thai waters, despite its high potential of dispersal. Limited gene flow levels (0.44-1.19 individuals per generation) of Thai P. pelagicus were also observed. A fine scale level of differentiation suggested that P. pelagicus from each geographic sample in Thai waters should be regarded as a separate genetic population and treated as a different exploited stock.

Isolation and characterization of genes specifically expressed in ovaries are necessary for understanding sex differentiation and ovarian development processes in the giant tiger shrimp, Penaeus monodon. In this study, a transcript that significantly matched the polehole precursor was further characterized by RACE-PCR. The sequence obtained was 5151 bp in length and contained a coding region of 5031 bp corresponding to 1677 amino acids. This transcript was only expressed in ovaries but not in testes of Juveniles (N = 10) and broodstock (N = 22) of P. monodon. A tissue distribution analysis further confirmed ovary-specific expression of this transcript (called P. monodon ovary-specific transcript 1, Pm-OST1) in female broodstock. Expression levels of Pm-OST 1 in ovaries of juvenile P. monodon upon 5-HT Injection (33.9+/-6.40 g; 50 microg/g body weight) were significantly higher at 12-72 hours post Injection (P<0.05). Quantitative real-time PCR Indicated that Pm-OST1 was comparably expressed throughout ovarian development in normal P. monodon broodstock (P>0.05). However, the expression level of Pm-OST1 was significantly higher in stage-III ovaries in eyestalk-ablated broodstock (P<0.05). Pm-OST1 was clearly localized in the ooplasm of previtellogenic and vitellogenic oocytes. Our results suggest that Pm-OST1 plays a functionally Important role in promoting the development of female germ cells and oocytes in P. monodon.

Most shrimp farmers in Chantaburi Province, Thailand, use water jets to dislodge sediment from empty pond bottoms, and wastewater is held for sedimentation before discharge into natural waters. Other pond bottom management practices used by a few farmers are sediment excavation, leave sediment but till entire pond bottom, and no mechanical treatment. All four methods of pond bottom treatment are followed by sun drying for 30 d. Soil organic carbon concentration in ponds following dry‐out seldom exceeded 2%. Although shrimp production in 24 ponds supplied by the same source of water was negatively correlated with increasing soil organic carbon concentration (r = −0.582), this observation does not confirm a causative relationship. Moreover, in trials conducted at Burapha University, Chantaburi Campus, bottom soil organic matter concentration following dry‐out differed little irrespective of treatment method. Lower soil moisture concentration revealed that dry‐out was more complete with sediment removal than without, but better dry‐out resulted in lower soil pH. Removal of sediment by excavation or flushing is expensive, and natural dry‐out combined with liming and occasional sediment removal should be investigated as a less expensive and more environment‐friendly alternative to removing sediment after each crop.

No abstract